1. Field of the Invention
The present invention relates to an information storage controller for high speed information transmission in a magnetic storage device or the like.
2. Description of the Prior Art
Recent development of digital compression technology of visual and audio signals makes it possible to process visual and audio signals by a computer and to store the signals in a magnetic storage device which can be accessed by a computer.
As to visual and audio signals, a problem often encountered is that an image or a sound is stopped when the processing of a prescribed amount of information is not completed in a prescribed time. In order to prevent this problem, a high speed magnetic storage device is required for high speed information processing.
Further, it is also required to increase a memory capacity and to store a large capacity of information. A technique called the redundant array of inexpensive disk (herein referred to as RAID) is used practically in order to meet this requirement.
A RAID is an information storage controller which controls a plurality of magnetic disks so that redundant information as well as information to be stored are stored in the magnetic disks in a distributed manner. When one of the magnetic disks fails, it can recover the information in the failed magnetic disk according to the redundant information. Then, a normal operation can be performed again.
RAID-5 (or RAID level 5), as one of the techniques of RAID, stores redundant information in a plurality of magnetic disks cyclicly. Let us assume that the information storage controller (RAID-5) has five magnetic disks HD1-HD5. Information to be written is divided into four sets of information D1-D4. First, the sets of information D1-D4 are written to four magnetic disks HD1-HD4, respectively, and redundant information P1 is generated for the sets of information D1-D4 to be written to the fifth magnetic disk HD5. Subsequently, when sets of information D5-D8 are written, the sets of information are written to HD2-HD5, while redundant information P2 for the sets of information D5-D8 is written to the first magnetic disk HD1. In this way, redundant information P1, P2, . . . are stored cyclicly to a magnetic disk which is different than the magnetic disk which stored the previous redundant information.
However, in the information storage controller, when information is written to a plurality of magnetic disks, redundant information has to be generated. Then, write operations may become slower than in a case using a single magnetic disk. Further, when one of the magnetic disks has a fault, processing speed becomes very slow in order to restore the information in the faulty magnetic disk. Further, when the faulty magnetic disk is changed with a new one, the information in the faulty magnetic disk has to be restored in the new one automatically. However, the operation speed becomes rather slow during this operation. This is ascribed to the work required to generate redundant information and to write it to a prescribed memory after the central processing unit reads data a plurality of times (sequential read). This work is performed for all the data, thus a long processing time is needed.
Further, in the prior art information storage controllers, work on each magnetic disk and an input/output operation with the external are performed in time sharing. That is, only one work is performed at a time.
An object of the invention is to provide an information storage controller having a higher speed of information transmission with magnetic storage devices.
The information storage controller according to the invention comprises an external communication means for communicating information with the external equipment; a plurality of magnetic disk communication means for communicating information with the magnetic disk; first and second groups each consisting of a plurality of memory devices, a number of the memory devices in said first and second groups being equal to that of the magnetic disk communication means; and a switch means for enabling communication between the second group and each of said magnetic disk communication means when communication between the first group and the external communication means is enabled and for enabling communication between the first group and each of the external communication means when communication between the second group and the external communication means is enabled. In the above-mentioned information storage controller, the first and second memory groups perform work with the external communication means or with the magnetic disk communication means alternately by the switch means, and each memory group performs work in parallel. Then, information transmission speed is improved.
An advantage of the present invention is that the write speed and read speed to and from the magnetic disks can be increased by using the first memory group, the second memory group, and the switch means for changing the state of work.
Further, another advantage of the present invention is that, by providing an exclusive redundant information generation circuit, generation of redundant information or verification and recovery of data can be performed at a fast speed, and parallel work by the switch means becomes more efficient in the information storage controller.